Glossary of Terms and Acronyms Used in the Design and Testing of Internal Combustion Engines

AAFI—Air-assisted fuel injection.

ABI—Advanced break-in.

Absorbed horsepower—Total horsepower absorbed by the absorption unit of the dynamometer and the friction components of the dynamometer.

Accelerated life test—Any set of test conditions designed to reproduce in a short time the effects encountered in the field.

Actual horsepower—The actual horsepower is the load horsepower that includes the friction in the dynamometer bearings and inertia simulation mechanism.

“A” curve—Maximum performance test.

Additive removal test—A test conducted by recirculating a specific additive type of oil through a test element for a specific period of time.

Aeration—The entrapment of gas in the coolant or oil.

After-boil—Boiling of the coolant after engine shutdown, caused by residual heat.

Air cleaner element—All airflow measurements are corrected to 25°C at 100 kPa standard test condition.

Air density—1.2250 kg/m3.

Air viscosity—1.7894 x 105Ns/m2.

Ambient—Used to denote surroundings, such as ambient temperature.

AQL—Acceptable quality level.

ATB—Air-to-boil temperature; the ambient temperature at which the coolant at the radiator reaches its boiling point.


Available secondary spark voltage—The minimum voltage at the spark terminal with the terminal open circuited and insulated from ground.

BAP—Barometric absolute pressure.

Basic engine—A runnable engine equipped with built-in accessories, fuel pump, oil pump, coolant pumps, emission control equipment, and all standard equip­ment as clearly defined by the individual manufacturer.

Bathtub curve—A bathtub-shaped plot of failure rate of an item (whether reparable or not) versus time; the failure rate initially decreases, then remains reasonably stable, and then begins to rise rapidly.

“B” curve—Production engine performance test.

Beachmarks—A term used to describe the characteristic fracture markings produced by fatigue crack propagation.

Beer-Lambert Law—For the purpose of diesel smoke measurement, an equation expressing the relationship between the opacity of a smoke plume, the effective optical path through the plume, and the opacity of the smoke per unit path length when:

K = attenuation coefficient (or actination)

L = path length through smoke in meters

Opacity = 1 — e~kl

N = 100(1 -e“kl)

K = 1/L 1 a( 1 — N/100) when L is expressed in meters

Best power—Power at maximum torque achievable by a given test multi-position small engine at the maximum continuous corrected net brake power speed.

Best straight line—A line midway between two parallel straight lines closest together and enclosing all output values on a calibration curve.


BIPO—Break-in and pass-off procedure (run-in).

BLA—Bottom limit advance.

Black smoke—Particles composed of carbon (soot), usually less than 1 |im in size.

BLD—Borderline detonation.

BMEP—Brake mean effective pressure.

BMEPc—Brake mean effective pressure corrected to a constant factor.

Boost pressure—The pressure of the charge of air as it leaves the turbocharger, super­charger, or other compressor.

Breakdown voltage (sparking plug)—The voltage at which a disruptive discharge takes place through or over the surface of the insulation.

Btu—British thermal unit.

°C—Degrees Centigrade.

Calibration curve (emissions)—A line drawn through at least seven points established by calibration gases, which determines the sensitivity of the analytical instrument to unknown gas concentrations.

Calibration traceability—The relation of a transducer calibration, through a specified step-by-step process, to an instrument or group of instruments calibrated by a national standards authority for each country.

Catalyst—A substance that accelerates a chemical reaction but which itself undergoes no permanent chemical change. For automotive emission purposes, catalysts are classified as oxidation catalysts (oxidize HC and CO) and reduction catalysts (reduce NOx) or three-way catalysts (oxidize HC and CO).

“C” curve—Performance as installed on the vehicle.

CFM—Cubic feet per minute.

Charging efficiency—The mass of delivered air retained in the cylinder (displaced volume times the ambient density).

Chemiluminescent (CL) analyzer—An instrument that measures nitric oxide by measuring the intensity of chemiluminescent radiation from the reaction of nitric oxide with ozone. The addition of a converter permits the measure­ment of oxides of nitrogen.

Cleanable element—A filter element, which when clogged can be restored by a suitable cleaning process to an acceptable percentage of its original flow/pressure differential characteristics.

Closed loop—A control system implementation in which information on output param­eters is used to improve the system accuracy or response.

Closed-loop circuit—Feedback system for controlling the air/fuel ratio (AFR).

Closed nozzle—A nozzle incorporating either a poppet valve or a needle valve loaded to open at some predetermined pressure; also a special type of needle valve wherein an integral pintle valve projection from the lower end of the needle is so formed as to influence the rate and shape of the fuel spray pattern during operation.

Closed nozzle valve—A needle valve having two diameters, the smaller at the valve seat.

The fuel injection pressure acting on a portion of the total valve area lifts the valve at a pre-determined pressure and then acts on the total area, while the end opposite of the valve seat is never subjected to injection pressure.

CO—Carbon monoxide.

C02—Carbon dioxide.

Coast down—The procedure used to determine the total horsepower absorbed by a chassis dynamometer at 50 mph; the time required for the chassis rollers to coast down from 50 mph to a pre-determined speed is noted, and from this, the rolling inertia forces can be calculated.

Coefficient of rolling resistance—The ratio of the rolling resistance to the vertical load.

Coefficient of variation—The standard deviation divided by the mean, multiplied by 100 and expressed as a percentage.

Coil interruption current—The peak current flowing through the coil primary winding at the time of interruption.

Cold start injector (CSI)—An auxiliary fuel injector that supplies additional fuel dur­ing cold cranking. Fuel injection generally is continuous, and the fuel rate is based on the orifice size, fuel pressure, and opening duration.

Combined life and partial—A filter life test in which specified amounts of retention test inorganic classified contaminants are admitted to the influent stream at specified intervals during the test to determine the particle separation efficiency of the filter at various stages of clogging.

Combustion chamber—An area of chamber divided by volume with the piston at top dead center.

Compression ratio—The maximum cylinder volume divided by the minimum cylinder volume.

Compressor efficiency—Isentropic total enthalpy rise across the compressor stage divided by the actual total enthalpy rise across the compressor stage.

Compressor pressure ratio—Outlet air absolute pressure divided by inlet air total absolute pressure.

Confidence coefficient—A measure of assurance that a statement based on statistical data is correct; the probability that an unknown parameter lies within a stated interval or is greater or less than some stated value.

Confidence level—Equals 1 — a, where a is the percent of risk.

Constant failure rate—A term characterizing the instantaneous failure rate in the middle of a bathtub curve or the useful life of a bathtub curve model of an item life.

Constant velocity joint—A universal joint that transmits rotational motion and angular velocity ratio of unity between the output and input shafts.

Constant volume sampler (CVD)—A device for collecting samples of diluted exhaust gas, where the exhaust gas is diluted with air in a manner that keeps the total flow rate of exhaust gas dilution air constant throughout the test. The device permits measuring mass emissions on a continuous basis and, through the use of a second pump, allows a proportional mass sample to be collected.

Contact pressure—The average pressure exerted by a seal on a shaft. This pressure is calculated by dividing the total lip force by the total lip contact area and sometimes is referred to as the radial pressure.

Continuous injection system—A fuel injection system in which fuel flows continu­ously from the injectors independent of cylinder events; a variable square law orifice frequently controls the flow rate.

Cool charge air temperature—The temperature of the cooled air entering the engine, commonly referred to as the intake manifold temperature or AIT.

Coolant—A liquid used for heat transfer and normally composed of 50% glycol and 50% water by volume.

CPS—Camshaft position sensor.

Curb weight—The weight of a vehicle in a drive-away condition, filled with at least 90% capacity by weight with fuel, lubricants, coolants, and all standard equipment, but without luggage or passengers.

Cyaniding—A case hardening process in which a ferrous material is heated above the lower transformation range in a molten state containing cyanide to cause simultaneous absorption of carbon and nitrogen at the surface and by dif­fusion creates a concentration gradient. Quench hardening completes the process.

De-aerating tank—A specially designed tank capable of removing entrained air or combustion gas from circulating coolant.

Decreasing failure rate—A term characterizing the instantaneous failure in the first period of the bathtub curve mode of product life.

Delivered air/fuel ratio—The mass of delivered air divided by the mass of delivered fuel.

Density recovery ratio—The ratio of the charge air density at the engine intake manifold to the air density at conditions of ambient temperature and boost pressure.

Diesel engine—Any compression ignition internal combustion engine using the basic diesel cycle, that is, combustion resulting from the spraying of fuel into air heated by compression.

Diesel smoke—Particles, including aerosols suspended in the gaseous exhaust stream of the engine, that obscure, reflect, or refract visible light.

Dilution factor—Based on a stoichiometric equation for fuel with composition CH1.85, the dilution factor as defined as

_________ UA_________

C02 + (HC + CO)xlO-4

Dilution tunnel—One of several types of ducts used to dynamically mix engine exhaust with dilution air in a stationary setup. Conditioned air supplied by a blower is mixed with engine exhaust at a mixing orifice in the upstream end of the tube, while sampling takes place at a downstream location.

Direct fuel injection (DFI)—Delivery of fuel directly into the combustion chamber.

Displacement—The volume required to extend the piston rod to its working stroke; the product of multiplying the area times the length of stroke, usually measured in cubic centimeters or cubic inches.

DOT—A flammable solid that is liable to cause fire through friction or can be readily ignited.

Double cardan universal joint—A near-constant velocity universal joint that consists of two cardan universal joints whose crosses are connected by a coupling yoke with internal supporting and centering means and which has intersecting shaft axes. At the design joint angle and at zero, the instantaneous angular velocity is zero (unity), while at other joint angles, it is near unity.

Drawdown—The quantity of coolant that can be lost before impairing cooling system performance, or grade cooling level, under normal operating conditions.

Driveline—An assembly of one or more driveshafts with provisions for axial movement, which transmits torque and/or rotary motion at a fixed or varying angular relationship from one shaft to another.

Driveline ratio—The crankshaft revolutions per minute divided by the revolutions per minute of traction wheels.


Durability—The probability that an item will operate as specified under stated condi­tions without a wear-out failure; a special case of reliability.

DVT—Design validation test. A test process to evaluate a design change.

Dynamometer—An energy-absorbing device designed to allow measured dynamic operation of the drivetrain of a vehicle while the vehicle remains stationary (chassis dynamometer).

EBP—Exhaust backpressure. The backpressure in an exhaust system.

Eddy currents—Those currents that exist as a result of voltages induced in a body of a conducting mass by a variation of magnetic flux. Note that the variation of magnetic flux is the result of a varying magnetic field or of a relative motion of the mass with respect to the magnetic field.

Electromagnetic compatibility (EMC)—The capability of electronic equipment of systems to be operated in the untended operational electromagnetic envi­ronment at designed levels of efficiency.

Electronic control unit (ECU)—An electronic module, one function of which is to calculate a command signal for the injector drive circuit, based on inputs from engine operating sensors.

Electronic fuel injection (EFI)—A general term referring to any fuel injection system in which fuel metering is controlled electronically. The quantity of fuel delivered is scheduled by an electronic control unit, and its output signal is based on information received from several sensors that monitor the operating conditions of the engine.

Excess air factor—The excess air factor can be expressed as

Trapped air — fuel ratio Stoichiometric ratio — air/fuel ratio

Exhaust gas oxygen sensor (EGOS)—A sensor located in the exhaust system that provides an electrical output that indicates oxygen content.

Exhaust gas recirculation (EGR)—A system that returns a portion of the exhaust gases to the combustion chamber, with the resulting lower combustion tempera­tures in turn reducing the formation of oxides and nitrogen.

°F—Degrees Fahrenheit.

Flame ionization detector (FID)—An analytical instrument used for determining the carbon concentration of hydrocarbons in a gas sample; a hydrogen-air dif­fusion flame detector that produces a signal proportional to the mass flow rate of hydrocarbons entering the flame per unit of time.

FMEP—Friction mean effective pressure.

Friction power—The power required to drive the engine alone as equipped for the power test. Friction power may be established by a number of methods including hot motoring friction where a friction torque is recorded at wide open throttle at each test speed point on the power test. All readings are taken at the same coolant and oil temperatures; Willans line; motoring tests. {See Willans line.)

GPD—General production design.



Hydrocarbons—All organic materials, including unbumed fuel and combustion by-products present in the exhaust, which are detected by a flame ioniza­tion detector.

Idle speed control (ISC)—A general term indicating any device or system that provides programmed control of engine idle speed.

IMEP—Indicated mean effective pressure.

Incremental filter efficiency—A method of calculating filter efficiency based on the total amount of contaminant presented to the filter during any specified segment of the test.

Indicated horsepower—The load horsepower that is set on the dynamometer and does not include the friction in the dynamometer bearings or inertia simulation mechanism.

In-line pump—An injection pump with two or more pumping elements arranged in line, with each pumping element serving only one cylinder.

Intake air temperature sensor (IATS)—A sensor that provides an electrical output proportional to the intake air temperature, and typically is mounted within or ahead of any airflow measuring device.

Intake manifold absolute pressure sensor (IMAPS)—A sensor that provides an electri­cal output proportional to the absolute pressure within the intake manifold downstream of the throttle plate.


LBT—Leanest fuel for best torque.

Light-off temperature—The temperature at which the conversion energy reaches a given value.

Loggery—Engine test log storage area.

MBT—Minimum spark (ignition advance) for best torque.

MBT-L—Minimum spark for best torque (MBT) retarded to clear borderline detonation.

Mean auto—Average of top and bottom limit advance settings.

Multi-pass oil cooler—An oil cooler that is circuited so that fluid passes either across or through the core more than once.

Net brake power—The measured power of a fully equipped engine.

NMEP—Net mean effective pressure.

Nobel metal catalyst—A catalyst in which the active material is made from a precious metal such as platinum, palladium, rhodium, or ruthenium.

Non-dispersive infrared analyzer (NDIR)—An instrument that, by absorption of infrared energy, selectively measures specific components.


OCT—Oil consumption test.

Original equipment manufacturer (OEM)—A component of the vehicle that was built according to the specification of the vehicle manufacturer and supplied in the vehicle at the time of original purchase of that vehicle can be said to be an OEM-compliant part.

Oxides of nitrogen (NOx)—The sum total of the nitric oxide and nitrogen oxide in a sample, expressed as nitrogen dioxide.

Parts per million (ppm)—Describing fractional defective, parts per million are obtained by multiplying the percent defective by 10,000 (e. g., 0.01% = 100 ppm).

PDG—Product development group.

PMEP—Pumping mean effective pressure.

Port opening—A term referring to a diesel fuel injection pump of the port and helix sleeve metering type in which the timing is determined by the point of the opening of the port by the metering member, corresponding to the nominal end of the pump delivery.

PTO—Power take-off.

PTO log—Record of PTO unit running hours. (PTO refers to the power take-off unit, fitted between the engine and the dynamometer.)

Rare earth catalyst—A catalyst in which the active material is a rare earth element such as lanthanum or cerium. Note that the rare earth elements range in atomic number from 57 to 71.

Rated net power—Engine net power at rated speed, as declared by the manufacturer.

Relative charge—The relative charge can be expressed as

Mass of trapped cylinder charge Displaced volume x Ambient density

Relative humidity—The ratio, expressed as a percentage, of the amount of water pres­ent in a given volume of air at a given temperature to the amount required to saturate the air at that temperature.

Scavenging efficiency—The scavenging efficiency can be expressed as

Mass of delivered air retained Mass of trapped cylinder charge

SFC—Specific fuel consumption.

SG—Specific gravity.

Specific fuel consumption (SFC)—Mass of fuel consumed per unit of work.

TLA—Top limit advance.

Torsional vibration damper—A torsionally tuned mechanical device that generally consists of an inertia ring attached to a drivetrain component by means of an elastomeric inner ring. It is tuned to a specific disturbing frequency.

Total oxides of nitrogen—The sum total of the measured parts per million (ppm) of nitric oxide (NO) plus the measured parts per million (ppm) of nitrogen dioxide (N02), expressed as an equivalent mass of N02.

Ultraviolet—Radiant energy having wavelengths of 0.4 to 0.04 jxm.

Valve overlap—Valve timing events are the valve opening and closing points in the operating cycle, whereas valve overlap describes that part of the cycle in which both the intake and exhaust valves are open.

Willan’s line—A method for estimating the friction power of a diesel engine.

[1] An engine crankshaft sensor generally has insufficient resolution, although 58x sys­tems are adequate for some rudimentary applications (58x = 58 pulses per crankshaft revolution).

— 360 pulses per revolution for general combustion work are preferred.

— 3600 pulses per revolution for knock work are preferred.

Figures 8.79 and 8.80 offer details about encoder troubleshooting.

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